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What heat effected or discoloured zones do you get?

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AdrianH
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What heat effected or discoloured zones do you get?

Postby AdrianH » Tue Mar 13, 2018 5:38 pm

This could be posted in the DIY section, but I guess it may not get read by many.

I was wondering if the heat affected zone along the edge of a cut could be an indication of good setup with Speeds and Amps.
The narrower the HAZ on the edge of a cut I would suspect the better, on my hobby system I get typically around 1mm discolouration on the edge of the cut of 1.5 mm steel. Not having a Hypertherm I can not work against Charts for my machine as there are none so I use guesswork and do not know if that is good or bad?

But, I think it could be of use to others as well, knowing what one should expect on a good system, may help gauge if you have the best set-up possible.

So would anyone like to say what they get, the perfect would be like some laser cut stuff I had done one could hardly see any HAZ edge at all.

So for each thickness of metal you cut what would you see?


Adrian
Last edited by AdrianH on Wed Mar 14, 2018 3:21 pm, edited 1 time in total.

jimcolt
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Re: What heat effected zones do you get?

Postby jimcolt » Wed Mar 14, 2018 8:43 am

The heat affected zone on steel will vary depending on the process (plasma torch, power level, air plasma or oxygen plasma, etc.). Most on this site use air plasma cutters, while other sites are more into the high definition industrial oxygen plasma for steel cutting.

With a Hypertherm air plasma when cutting steel...there is a zone that will often show a heat shadow (with very little effect on the hardness and weldability of the cut edge) however air produces a chemical effect called nitriding (air is 80% nitrogen) that will harden the edge in the range of .006" to .010" in from the cut edge. This assumes you are following cut specs as listed in the cut charts in the Hypertherm operators manual. Slower cut speeds, worn out consumables, higher cut height, higher amperage will alter the heat affected zone.

On many steels you cannot see a heat affected zone, on some (cold rolled, P&O usually) you will see a heat shadow. If the shadow changes throughout the cut (gets wide in some areas and is narrow in others) it is likely due to speed changes (slowing down for cornering and details). CNC machines with higher acceleration rates will minimize varaiation in the heat affected zone width. Generally...machines with inadequately sized drive motors, gantries and torch carriages that are heavy will produce widely varying heat affected zones, while better machine designs (Matched motors, gearing and mass of moving parts) will provide better results.

The nitride hardening affects weldability and machineability of a plasma cut edge. since it usually is only .006" wide it can be removed with a grinder easily. Since you mention laser cutting (high cost industrial process).....perhaps you should consider high definition oxygen plasma....with no nitriding, 100% weldable edge, minimal hardening and a smaller heat affected zone. Note that you cannot use oxygen in an air plasma torch.

Best bet for understanding heat affected zone widths produced on your machine is to cut some samples and get them evaluated at a test lab.

Jim Colt Hypertherm

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AdrianH
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Re: What heat effected zones do you get?

Postby AdrianH » Wed Mar 14, 2018 1:56 pm

Hello Jim, thanks for the response.

I guess I was aiming more for the air compressed air systems people use on here. And that zone you mention when using the Hypertherm, the discoloured area, or heat shadow as you describe it as is what I was wondering. Not the Nitrated edge hardening that would be hard for anyone to really determine.
And not laser, that I mentioned as I had some material laser cut and I could not see the any discoloured zone at all, and as you say the initial cost of systems is lots.
So if someone cuts 1/4 inch, how wide is it, if some one cuts 1/2 inch how wide etc. Get a consensus, would it give useful information to others, home builders and anyone not using a Hypertherm, such as Miller, Cebora, Chinese etc.

It may not be a perfect idea, I was just thinking that if one can cut an edge and get say a 1/16 inch wide zone, another can look at theirs and think mines wider, can I speed up or use less amps.
Yes I do agree it also depends on the metal being cut, Hot rolled would be difficult to see, cold rolled easier, that bit I had not considered.

Cheers

Adrian


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